Melt processable starch compositions

ABSTRACT

The present invention relates to a starch composition comprising starch, a polymer that is substantially compatible with starch and has a weight-average molecular weight of at least 500,000 such that the polymer forms effective entanglements or associations with neighboring starch molecules, and preferably at least one additive to improve melt flow and melt processability. The additive may be a hydroxyl plasticizer, a hydroxyl-free plasticizer, a diluent, or mixtures thereof. The composition is melt processable on conventional thermoplastic equipment. The composition is especially suitable for uniaxial and biaxial extensional processes to make fibers, films, foams and like products.

This application is a continuation-in-part of application Ser. No.09/264,401 filed on Mar. 8, 1999, now abandoned, and claims the benefitthereof and incorporates the same by reference.

FIELD OF INVENTION

This invention relates a novel starch composition that is substantiallyhomogenous and has desirable rheological characteristics such that it ismelt processable by conventional thermoplastic processing equipment. Thepresent composition is particularly suitable for uniaxial and biaxialextensional processes.

BACKGROUND OF THE INVENTION

It is well recognized that starch molecules come in two forms: thesubstantially linear amylose polymer and the highly branched amylopectinpolymer. These two forms of starch have very different properties,probably due to the ease of association of the hydroxyl groups amongdifferent molecules. The molecular structure of amylose is essentiallylinear with two to five relatively long branches. The average degree ofpolymerization of the branches is about 350 monomer units. Underconditions that provide sufficient freedom of molecular movements,primarily by dilution with suitable solvents, and in some instances,dilution coupled with heating, the linear amylose chains can be orientedinto preferentially parallel alignments such that the hydroxyl groups onone chain are in close proximity with those on the adjacent chains. Thealignment of neighboring amylose molecules is believed to facilitateintermolecular hydrogen bonding. Consequently the amylose molecules formstrong aggregates. In contrast, the molecular structure of amylopectinis highly branched via 1,6-α linkages. The average degree ofpolymerization of the branches is about 25 monomer units. Due to thehighly branched structure, the amylopectin molecules can not move asfreely and do not align and associate as readily.

Attempts have been made to process natural starch on standard equipmentand existing technology known in the plastic industry. Since naturalstarch generally has a granular structure, it needs to be destructurizedand/or modified before it can be melt processed like a thermoplasticmaterial. For destructurization, the starch is typically heated aboveits softening and melting temperature under a pressurized condition.Melting and disordering of the molecular structure of the starch granuletakes place and a destructurized starch is obtained. Chemical orenzymatic agents may also be used to destructurize, oxidize, orderivatize the starch. Modified starches have been used to makebiodegradable plastics, wherein the modified starch is blended as anadditive or the minor component with petroleum-based or syntheticpolymers. However, when the modified starch is processed by itself or asthe major component in a blend with other materials using conventionalthermoplastic processing techniques, such as molding or extrusion, thefinished parts tend to have a high incidence of defects. Moreover, themodified starch (alone or as the major component of a blend) has beenfound to have poor melt extensibility; consequently, it cannot besuccessfully processed by uniaxial or biaxial extensional processes intofibers, films, foams or the like.

Previous attempts to produce starch fibers relate principally towet-spinning processes. For Example, a starch/solvent colloidalsuspension can be extruded from a spinneret into a coagulating bath.This process relies on the marked tendency of amylose to align and formstrongly associated aggregates to provide strength and integrity to thefinal fiber. Any amylopectin present is tolerated as an impurity thatadversely affects the fiber spinning process and the strength of thefinal product. Since it is well known that natural starch is rich inamylopectin, earlier approaches include pre-treating the natural starchto obtain the amylose-rich portion desirable for fiber spinning. Clearlythis approach is not economically feasible on a commercial scale since alarge portion (i.e, the amylopectin portion) of the starch is discarded.In more recent developments, natural starch, typically high in naturalamylopectin content, can be wet-spun into fibers. However, the wet-spunfibers are coarse, typically having fiber diameters greater than 50microns. Additionally, the large quantity of solvent used in thisprocess requires an additional drying step and a recovery or treatmentstep of the effluent. Some references for wet-spinning starch fibersinclude U.S. Pat. No. 4,139,699 issued to Hernandez et al. on Feb. 13,1979; U.S. Pat. No. 4,853,168 issued to Eden et al. on Aug. 1, 1989; andU.S. Pat. No. 4,234,480 issued to Hernandez et al. on Jan. 6, 1981.

U.S. Pat. Nos. 5,516,815 and 5,316,578 to Buehler et al. relate tostarch compositions for making starch fibers from a melt spinningprocess. The melt starch composition is extruded through a spinneretteto produce filaments having diameters slightly enlarged relative to thediameter of the die orifices on the spinnerette (i.e., a die swelleffect). The filaments are subsequently drawn down mechanically orthermomechanically by a drawing unit to reduce the fiber diameter. Themajor disadvantage of the starch composition of Buehler et al. is thatit does not use high molecular weight polymers, which enhance the meltextensibility of starch compositions. Consequently, the starchcomposition of Buehler et al. could not be successfully melt attenuatedto produce fine fibers of 25 microns or less in diameter.

Other thermoplastically processable starch compositions are disclosed inU.S. Pat. No. 4,900,361, issued on Aug. 8, 1989 to Sachetto et al.; U.S.Pat. No. 5,095,054, issued on Mar. 10, 1992 to Lay et al.; U.S. Pat. No.5,736,586, issued on Apr. 7, 1998 to Bastioli et al.; and PCTpublication WO 98/40434 filed by Hanna et al. published Mar. 14, 1997.These starch compositions do not contain the high molecular weightpolymers that are necessary to achieve the desired melt viscosity andmelt extensibility, which are critical material characteristics toproducing fine fibers, thin films or thin-walled foams.

The art shows a need for an inexpensive and melt processable compositionfrom natural starches. Such a melt processable starch composition shouldnot require evaporation of a large quantity of solvents or produce alarge amount of effluent during the processing operation. Moreover, sucha starch composition should have melt Theological properties suitablefor use in conventional plastic processing equipment

The art also shows a need for a starch composition suitable for use inuniaxial or biaxial extensional processes to produce fibers, films,sheets, foams, shaped articles, and the like economically andefficiently. Specifically, the starch composition should have meltrheological properties suitable for uniaxial or biaxial extensionalprocesses in its melt phase in a substantially continuous manner, i.e.,without excessive amount of melt fracture or other defects.

SUMMARY OF THE INVENTION

The present invention relates to a starch composition that is meltprocessable on conventional thermoplastic equipment. Specifically, thestarch composition may be successfully processed via uniaxial or biaxialextensional forces to provide a final product with good strength.Moreover the starch composition has rheological properties suitable foruse in melt attenuation processes to achieve very high uniaxial orbiaxial extensions, which are generally not achievable by otherprocesses, including jet or mechanical elongation processes.

The present invention relates to a starch composition comprising starch,a polymer that is substantially compatible with starch and has amolecular weight sufficiently high to form effective entanglements orassociations with neighboring starch molecules, and preferably at leastone additive to improve melt flow and melt processability. Polymershaving a weight-average molecular weight of at least 500,000 areparticularly useful herein. The additive may be a hydroxyl plasticizer,a hydroxyl-free plasticizer, a diluent, or mixtures thereof.

The starch compositions of the present invention have the combination ofmelt strength and melt viscosities (shear and extensional) in thedesired range such that the compositions are uniquely suitable for themelt extensional processes. The starch composition of the presentinvention typically has a melt shear viscosity in the range of about 0.1to about 40 Pa·s so that the composition can be mixed, conveyed orotherwise processed on conventional processing equipment, includingscrew extruders, stir tanks, pumps, spinnerets, and the like. The starchcomposition of the present invention typically has an enhanced meltextensional viscosity due to the incorporation of the high polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a torque rheometer assembly having a melt blowing die usedto produce fine starch fibers of the present invention.

FIG. 2 shows a torque rheometer assembly used to produce starch fiberweb by spun bonding.

FIG. 3a is the Scanning Electron Micrographs of fine starch fibers ofthe present invention shown on a 200 micron scale.

FIG. 3b is the Scanning Electron Micrographs of fine starch fibers ofthe present invention shown on a 20 micron scale.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “comprising” means that the various components,ingredients, or steps, can be conjointly employed in practicing thepresent invention. Accordingly, the term “comprising” encompasses themore restrictive terms “consisting essentially of” and “consisting of.”

As used herein, the term “bound water” means the water found naturallyoccurring in starch and before starch is mixed with other components tomake the composition of the present invention. The term “free water”means the water that is added in making the composition of the presentinvention. A person of ordinary skill in the art would recognize thatonce the components are mixed in a composition, water can no longer bedistinguished by its origin.

All percentages, ratios and proportions used herein are by weightpercent of the composition, unless otherwise specified.

The Starch Compositions

Naturally occurring starch is generally a mixture of linear amylose andbranched amylopectin polymer of D-glucose units. The amylose is asunstantially linear polymer of D-glucose units joined by (1,4)-α-Dlinks. The amylopectin is a highly branched polymer of D-glucose unitsjoined by (1,4)-α-D links and (1,6)-α-D links at the branch points.Naturally occurring starch typically contain relatively highamylopectin, for example, corn starch (64-80% amylopectin), waxy maize(93-100% amylopectin), rice (83-84% amylopectin), potato (about 78%amylopectin), and wheat (73-83% amylopectin). Though all starches areuseful herein, the present invention is most commonly practiced withhigh amylopectin natural starches derived from agricultural sources,which offer the advantages of being abundant in supply, easilyreplenishable and inexpensive.

Suitable for use herein are any naturally occurring unmodified starchesand modified starches; the starch may be modified by physical, chemical,or biological processes, or combinations thereof. The choice ofunmodified or modified starch for the present invention may depend onthe end product desired. Also suitable for use herein are mixtures ofvarious starches, as well as mixtures of the amylose or amylopectinfractions, having an amylopectin content in the desirable range. Thestarch or starch mixture useful in the present invention typically hasan amylopectin content from about 20% to about 100%, preferably fromabout 40% to about 90%, more preferably from about 60% to about 85% byweight of the starch or mixtures thereof.

Suitable naturally occurring starches can include, but are not limitedto, corn starch, potato starch, sweet potato starch, wheat starch, sagopalm starch, tapioca starch, rice starch, soybean starch, arrow rootstarch, amioca starch, bracken starch, lotus starch, waxy maize starch,and high amylose corn starch. Naturally occurring starches particularly,corn starch and wheat starch, are the preferred starch polymers due totheir economy and availability.

Physical modifications of the starch may be intramolecular orintermolecular modifications. Intramolecular modifications includereduced molecular weight and/or molecular weight distribution, changesin the polymer chain conformation, and the like. Intermolecularmodifications include melting and/or disordering the starch molecules,reduction in crystallinity, crystallite size, and granular size, and thelike. These physical modifications may be achieved by input of energy(such as thermal, mechanical, thermomechanical, electromagnatic,ultrasonic, and the like), pressure, moisture, fractionation, andcombinations thereof.

Chemical modifications of starch typically include acid or alkalihydrolysis and oxidative chain scission to reduce molecular weight andmolecular weight distribution. Suitable compounds for chemicalmodification of starch include organic acid such as citric acid, aceticacid, glycolic acid, and adipic acid; inorganic acids such ashydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boricacid, and partial salts of polybasic acids, e.g., KH₂PO₄, NaHSO₄; groupIa or IIa metal hydroxides such as sodium hydroxide, and potassiumhydroxide; ammonia; oxidizing agents such as hydrogen peroxide, benzoylperoxide, ammonium persulfate, potassium permagnate, sodium bicarbonate,hypochloric salts, and the like; and mixtures thereof. Preferredchemical agents of the present invention include ammonium persulfate,sulfuric acid, hydrochloric acid, and mixtures thereof.

Chemical modifications may also include derivatization of starch byreaction of its OH groups with alkylene oxides, and other ether-,ester-, urethane-, carbamate-, or isocyanate-forming substances.Hydroxylalkyl, acetyl, or carbamate starches or mixtures thereof arepreferred chemically modified starches. The degree of substitution ofthe chemically modified starch is 0.05 to 3.0, preferably 0.05 to 0.2.

Biological modifications of starch include bacterial digestion of thecarbohydrate bonds, or enzymatic hydrolysis using enzymes such asamylase, amylopectase, and the like.

The starch typically has a bound water content of about 5% to 16% byweight of starch. A water content of about 8% to about 12% by weight ofstarch is particularly preferred. The amylose content of the starch istypically from 0% to about 80%, preferably from about 20% to about 35%,by weight of starch.

Natural, unmodified starch generally has a very high average molecularweight and a broad molecular weight distribution (e.g. natural cornstarch has an average molecular weight of about 10,000,000 and amolecular weight distribution greater than 1000). The average molecularweight of starch can be reduced to the desirable range for the presentinvention by chain scission (oxidative or enzymatic), hydrolysis (acidor alkaline catalyzed), physical/mechanical degradation (e.g., via thethermomechanical energy input of the processing equipment), orcombinations thereof. These reactions also reduce the molecular weightdistribution of starch to less than about 600, preferably to less thanabout 300. The thermomechanical method and the oxidation method offer anadditional advantage in that they are capable of being carried out insitu of the melt spinning process.

In one embodiment, the natural starch is hydrolyzed in the presence ofacid, such as hydrochloric acid or sulfuric acid, to reduce themolecular weight and molecular weight distribution. In anotherembodiment, a chain scission agent may be incorporated into the meltspinnable starch composition such that the chain scission reaction takesplace substantially concurrently with the blending of the starch withother components. Nonlimiting examples of oxidative chain scissionagents suitable for use herein include ammonium persulfate, hydrogenperoxide, hypochlorate salts, potassium permanganate, and mixturesthereof. Typically, the chain scission agent is added in an amounteffective to reduce the weight-average molecular weight of the starch tothe desirable range. For example, it is found that for uniaxial orbiaxial melt attenuation processes, the starch should have aweight-average molecular weight ranging from about 1,000 to about2,000,000, preferably from about 1,500 to about 800,000, more preferablyfrom about 2,000 to about 500,000. It is found that compositions havingmodified starch in the above molecular weight range have a suitable meltshear viscosity, and thus improved melt processability. The improvedmelt processability is evident in less interruptions of the process(e.g., reduced breakage, shots, defects, hang-ups) and better surfaceappearance and strength properties of the product.

Typically the composition herein comprises from about 20 to about 99.99wt %, preferably from about 30 to about 95 wt %, and more preferablyfrom about 50 to about 85 wt %, of unmodified and/or modified starch.The weight of starch in the composition includes starch and itsnaturally occurring bound water content. It is known that additionalfree water may be incorporated as the polar solvent or plasticizer, andnot included in the weight of the starch.

High molecular weight polymers (hereinafter “high polymers”) which aresubstantially compatible with starch are also useful herein. Themolecular weight of a suitable polymer should be sufficiently high toeffectuate entanglements and/or associations with starch molecules. Thehigh polymer preferably has a substantially linear chain structure,though a linear chain having short (C1-C3) branches or a branched chainhaving one to three long branches are also suitable for use herein. Asused herein, the term “substantially compatible” means when heated to atemperature above the softening and/or the melting temperature of thecomposition, the high polymer is capable of forming a substantiallyhomogeneous mixture with the starch (i.e., the composition appearstransparent or translucent to the naked eye).

The Hildebrand solubility parameter (δ) can be used to estimate thecompatibility between starch and the polymer. Generally, substantialcompatibility between two materials can be expected when theirsolubility parameters are similar. It is known that water has aδ_(water) value of 48.0 MPa^(1/2), which is the highest among commonsolvents, probably due to the strong hydrogen bonding capacity of water.Starch typically has a δ_(starch) value similar to that of cellulose(about 34 MPa^(1/2)).

Without being bound by theory, it is believed that polymers suitable foruse herein preferably interact with the starch molecules on themolecular level in order to form a substantially compatible mixture. Theinteractions range from the strong, chemical type interactions such ashydrogen bonding between polymer and starch, to merely physicalentanglements between them. The polymers useful herein are preferablyhigh molecular weight, substantially linear chain molecules. The highlybranched structure of a amylopectin molecule favors the branches tointeract intramolecularly, due to the proximity of the branches within asingle molecule. Thus, it is believed that the amylopectin molecule haspoor or ineffective entanglements/interactions with other starchmolecules, particularly other amylopectin molecules. The compatibilitywith starch enables suitable polymers to be intimately mixed andchemically interact and/or physically entangle with the branchedamylopectin molecules such that the amylopectin molecules associate withone another via the polymers. The high molecular weight of the polymerenables it to simultaneously interact/entangle with several starchmolecules. That is, the high polymers function as molecular links forstarch molecules. The linking function of the high polymers isparticularly important for starches high in amylopectin content. Theentanglements and/or associations between starch and polymers enhancethe melt extensibility of the starch composition such that thecomposition is suitable for extensional processes. In one embodiment, itis found that the composition can be melt attenuated uniaxially to avery high draw ratio (greater than 1000).

In order to effectively form entanglements and/or associations with thestarch molecules, the high polymer suitable for use herein should have aweight-average molecular weight of at least 500,000. Typically theweight average molecular weight of the polymer ranges from about 500,000to about 25,000,000, preferably from about 800,000 to about 22,000,000,more preferably from about 1,000,000 to about 20,000,000, and mostpreferably from about 2,000,000 to about 15,000,000. The high molecularweight polymers are preferred due to the ability to simultaneouslyinteract with several starch molecules, thereby increasing extensionalmelt viscosity and reducing melt fracture.

Suitable high polymers have a δ_(polymer) such that the differencebetween δ_(starch) and δ_(polymer) is less than about 10 MPa^(1/2),preferably less than about 5 MPa^(1/2), and more preferably less thanabout 3 MPa^(1/2). Nonlimiting examples of suitable high polymersinclude polyacrylamide and derivatives such as carboxyl modifiedpolyacrylamide; acrylic polymers and copolymers including polyacrylicacid, polymethacrylic acid, and their partial esters; vinyl polymersincluding polyvinyl alcohol, polyvinylacetate, polyvinylpyrrolidone,polyethylene vinyl acetate, polyethyleneimine, and the like; polyamides;polyalkylene oxides such as polyethylene oxide, polypropylene oxide,polyethylenepropylene oxide, and mixtures thereof. Copolymers made frommixtures of monomers selected from any of the aforementioned polymersare also suitable herein. Other exemplary high polymers include watersoluble polysaccharides such as alginates, carrageenans, pectin andderivatives, chitin and derivatives, and the like; gums such as guargum, xanthum gum, agar, gum arabic, karaya gum, tragacanth gum, locustbean gum, and like gums; water soluble derivatives of cellulose, such asalkylcellulose, hydroxyalkylcellulose, carboxyalkylcellulose, and thelike; and mixtures thereof.

Some polymers (e.g., polyacrylic acid, polymethacrylic acid) aregenerally not available in the high molecular weight range (i.e.,500,000 or higher). A small amount of crosslinking agents may be addedto create branched polymers of suitably high molecular weight usefulherein.

The high polymer is added to the composition of the present invention inan amount effective to visibly reduce the melt fracture and capillarybreakage of fibers during the spinning process such that substantiallycontinuous fibers having relatively consistent diameter can be meltspun. These polymers are typically present in the range from about 0.001to about 10 wt %, preferably from about 0.005 to about 5 wt %, morepreferably from about 0.01 to about 1 wt %, and most preferably fromabout 0.05 to about 0.5 wt % of the composition. It is surprising tofind that at a relatively low concentration, these polymerssignificantly improve the melt extensibility of the starch composition.

The starch compositions may optionally include additives to enhance meltflow and melt processability, particularly the extensibility of thecomposition under the melt processing conditions. The additives mayfunction as plasticizers and/or diluents to reduce the melt shearviscosity of the starch composition. The plasticizers are added to thecomposition of the present invention in an amount effective to improvethe flow, hence, the melt processability. The plasticizers may alsoimprove the flexibility of the final products, which is believed to bedue to the lowering of the glass transition temperature of thecomposition by the plasticizer. The plasticizers should preferably besubstantially compatible with the polymeric components of the presentinvention so that the plasticizers may effectively modify the propertiesof the composition. As used herein, the term “substantially compatible”means when heated to a temperature above the softening and/or themelting temperature of the composition, the plasticizer is capable offorming a substantially homogeneous mixture with starch (i.e., thecomposition appears transparent or translucent to the naked eye).

Suitable for use herein as hydroxyl plasticizers are organic compoundshaving at least one hydroxyl group, preferably a polyol. Without beingbound by theory, it is believed that the hydroxyl groups of theplasticizers enhance compatibility by forming hydrogen bonds with thestarch matrix material. Nonlimiting examples of useful hydroxylplasticizers include sugars such as glucose, sucrose, fructose,raffinose, maltodextrose, galactose, xylose, maltose, lactose, mannose,erythrose, glycerol, and pentaerythritol; sugar alcohols such aserythritol, xylitol, maltitol, mannitol and sorbitol; polyols such asethylene glycol, propylene glycol, dipropylene glycol, butylene glycol,hexane triol, and the like, and polymers thereof; and mixtures thereof.

Also useful herein as hydroxyl plasticizers are poloxomers(polyoxyethylene/polyoxypropylene block copolymers) and poloxamines(polyoxyethylene/polyoxypropylene block copolymers of ethylene diamine).Suitable “poloxomers” comprise block copolymers ofpolyoxyethylene/polyoxypropylene having the following structure:

HO—(CH₂—CH₂—O)_(x)—(CHCH₃—CH₂—O)_(y)—(CH₂—CH₂—O)_(z)—OH

wherein x has a value ranging from about 2 to about 40, y has a valueranging from about 10 to about 50, and z has a value ranging from about2 to about 40, and preferably x and z have the same value. Thesecopolymers are available as Pluronic® from BASF Corp., Parsippany, N.J.Suitable poloxamers and poloxamines are available as Synperonic® fromICI Chemicals, Wilmington, Del., or as Tetronic® from BASF Corp.,Parsippany, N.J.

Also suitable for use herein as hydroxyl-free plasticizers are otherhydrogen bond forming organic compounds which do not have hydroxylgroup, including urea and urea derivatives; anhydrides of sugar alcoholssuch as sorbitan; animal proteins such as gelatin; vegetable proteinssuch as sunflower protein, soybean protein, and cotton seed protein; andmixtures thereof. All of the plasticizers may be used alone or inmixtures thereof.

Typically, the hydroxyl plasticizer comprises from about 1 wt % to about70 wt %, more preferably from about 2 wt % to about 60 wt %, mostpreferably from about 3 wt % to about 40 wt % of the starch composition.The hydroxyl-free plasticizer typically comprises from about 0.1 wt % toabout 70 wt %, preferably from about 2 wt % to about 50 wt %, morepreferably from about 3 wt % to about 40 wt % of the starch composition.

In one embodiment, a mixture of the hydroxyl and hydroxyl-freeplasticizers is used, wherein the hydroxyl plasticizers are sugars, suchas sucrose, fructose, and sorbitol, and the hydroxyl-free plasticizersare urea and urea derivatives. It is found that urea and its derivativesin the starch composition of the present invention have a strongtendency to crystallize, that is, crystallization of urea and itsderivatives occurs even under fast cooling condition such as meltblowing, spun bonding, melt extrusion, wet spinning, and the like.Therefore, urea and urea derivatives may be used as solidifying agentsfor modifying or controlling the solidification rate of the starchcomposition of the present invention. In a preferred embodiment, amixture of sucrose and urea is added to the starch/polymer compositionin an amount effective to achieve the desired melt processability andsolidification rate.

Diluents such as polar solvents may be added to the starch compositionsof the present invention to adjust the melt shear viscosity and enhancethe melt spinnability of the starch compositions. Generally, the meltshear viscosity decreases in a nonlinear manner as the diluent contentis increased. Typically, the diluent is added in an amount from about 5wt % to about 60 wt %, preferably from about 7 wt % to about 50 wt %,more preferably from about 10 wt % to about 30 wt %, of the totalcomposition.

Suitable for use herein as diluents are polar solvents having asolubility parameter δ ranging from about 19 to about 48 MPa^(1/2),preferably from about 24 to about 48 MPa^(1/2), and more preferably fromabout 28 to about 48 MPa^(1/2). Nonlimiting examples include water,C1-C18 linear or branched alcohols, DMSO (dimethyl sulphoxide),formamide and derivatives such as N-methyl formamide, N-ethyl formamide,acetamide and derivatives such as methyl acetamide, Cellosolv® (a glycolalkyl ether) and derivatives, such as butyl Cellosolv®, benzylCellosolv®, Cellosolv® acetate (all Cellosolv® and derivatives areavailable from J. T. Baker, Phillipsburg, N.J.), hydrazine, and ammonia.It is also known that the δ value of a solvent mixture can be determinedby volume-averaging the δ values of the individual solvents. Therefore,mixed solvents having δ values within the above-identified range (i.e.,from about 19 to about 48 MPa^(1/2)) are also suitable for use herein.For example, a mixed solvent of DMSO/water having a composition of 90/10v/v would have a δ value of about 31.5; such a mixed solvent system issuitable for use herein.

It is found that polar solvents capable of forming hydrogen bonding aremore effective in lowering the melt viscosity of the composition. Assuch, a lower amount of the polar solvent is sufficient to adjust theviscosity to the desired range for melt spinning. Using a lower amountof the polar solvent provides a further advantage of reducing the needfor an evaporation step during or subsequent to the melt processingstep, which results in operating cost advantages such as lower energyconsumption and lower solvent recovery costs, as well as lower costs forenvironmental/regulatory compliance.

The starch composition may optionally include liquid or volatileprocessing aids which function mainly as viscosity modifiers of the meltcompositions. The processing aid is substantially volatized and removedduring the melt processing stage such that only a residual/trace amountremains in the final product. Thus, they do not adversely affect thestrength, modulus or other properties of the final product. The polarsolvents disclosed above may also function as volatile processing aids.Other nonlimiting examples include carbonates such as sodiumbicarbonate.

Optionally, other ingredients may be incorporated into the spinnablestarch composition to modify the processability and/or to modifyphysical properties such as elasticity, tensile strength and modulus ofthe final product. Nonlimiting examples include oxidation agents,cross-linking agents, emulsifiers, surfactants, debonding agents,lubricants, other processing aids, optical brighteners, antioxidants,flame retardants, dyes, pigments, fillers, proteins and their alkalisalts, biodegradable synthetic polymers, waxes, low melting syntheticthermoplastic polymers, tackifying resins, extenders, wet strenth resinsand mixtures thereof. These optional ingredients may be present inquantities ranging from about 0.1% to about 70%, preferably from about1% to about 60%, more preferably from about 5% to about 50%, and mostpreferably from about 10% to about 50%, by weight of the composition.

Exemplary biodegradable synthetic polymers include polycaprolactone;polyhydroxyalkanoates including polyhydroxybutyrates, andpolyhydroxyvalerates; polylactides; and mixtures thereof.

Lubricant compounds may further be added to improve the flow propertiesof the starch material during the processes used for producing thepresent invention. The lubricant compounds can include animal orvegetable fats, preferably in their hydrogenated form, especially thosewhich are solid at room temperature. Additional lubricant materialsinclude mono-glycerides and di-glycerides and phosphatides, especiallylecithin. For the present invention, a preferred lubricant compoundincludes the mono-glyceride, glycerol mono-stearate.

Further additives including inorganic particles such as the oxides ofmagnesium, aluminum, silicon, and titanium may be added as inexpensivefillers or extenders. Additionally, additives such as inorganic salts,including alkali metal salts, alkaline earth metal salts, phosphatesalts, etc., may be used.

Other additives may be desirable depending upon the particular end useof the product contemplated. For example, in products such as toilettissue, disposable towels, facial tissues and other similar products,wet strength is a desirable attribute. Thus, it is often desirable toadd to the starch polymer cross-linking agents known in the art as “wetstrength” resins.

A general dissertation on the types of wet strength resins utilized inthe paper art can be found in TAPPI monograph series No. 29, WetStrength in Paper and Paperboard, Technical Association of the Pulp andPaper Industry (New York, 1965). The most useful wet strength resinshave generally been cationic in character. Polyamide-epichlorohydrinresins are cationic polyamide amine-epichlorohydrin wet strength resinswhich have been found to be of particular utility. Suitable types ofsuch resins are described in U.S. Pat. No. 3,700,623, issued on Oct. 24,1972, and U.S. Pat. No. 3,772,076, issued on Nov. 13, 1973, both issuedto Keim and both being hereby incorporated by reference. One commercialsource of a useful polyamide-epichlorohydrin resin is Hercules, Inc. ofWilmington, Del., which markets such resins under the mark Kymene®.

Glyoxylated polyacrylamide resins have also been found to be of utilityas wet strength resins. These resins are described in U.S. Pat. No.3,556,932, issued on Jan. 19, 1971, to Coscia, et al. and U.S. Pat. No.3,556,933, issued on Jan. 19, 1971, to Williams et al., both patentsbeing incorporated herein by reference. One commercial source ofglyoxylated polyacrylamide resins is Cytec Co. of Stanford, Conn., whichmarkets one such resin under the mark Parez® 631 NC.

It is found that when suitable cross-linking agent such as Parez® 631NCis added to the starch composition of the present invention under acidiccondition. The composition is rendered water insoluble. That is, thewater solubility of the composition, as tested by the Test Methoddescribed hereinafter, is less than 30%, preferably less than 20%, morepreferably less than 10% and most preferably less than 5%. The productssuch as fibers and films made from such a composition are also waterinsoluble.

Still other water-soluble cationic resins finding utility in thisinvention are urea formaldehyde and melamine formaldehyde resins. Themore common functional groups of these polyfunctional resins arenitrogen containing groups such as amino groups and methylol groupsattached to nitrogen. Polyethylenimine type resins may also find utilityin the present invention. In addition, temporary wet strength resinssuch as Caldas® 10 (manufactured by Japan Carlit) and CoBond® 1000(manufactured by National Starch and Chemical Company) may be used inthe present invention.

For the present invention, a suitable cross-linking agent is added tothe composition in quantities ranging from about 0.1% by weight to about10% by weight, more preferably from about 0.1% by weight to about 3% byweight.

The Rheology of The Starch Compositions

The rheological behavior of the starch composition is an importantconsideration for selecting suitable materials and fabricationequipment/processes. Many factors contribute to the rheological behaviorof the starch composition, including the amount and the type ofpolymeric components used, the molecular weight and molecular weightdistribution of the components, the amount and type of additives (e.g.,plasticizers, processing aids), the processing conditions such astemperature, pressure, rate of deformation, and relative humidity, andin the case of non-Newtonian materials, the deformation history (i.e., atime or strain history dependence).

The starch composition of the present invention typically has a highsolid content (i.e., a concentration above a critical concentration C*)such that a dynamic or fluctuating entangled network is formed whereinthe starch molecules and the high polymers become associated anddisassociated temporally. The association may be in the form of physicalentanglements, van der Waals forces, or chemical interactions such ashydrogen bonding. The starch composition having the entangled networkstructure exhibits melt flow behavior typical of a non-Newtonian fluid.

The starch composition of the present invention may exhibit a strainhardening behavior, that is, the extensional viscosity increases as thestrain or deformation increases. Typically, a Newtonian fluid exhibit alinear relationship between stress/force and strain. That is, there isno strain hardening behavior in a Newtonian fluid. On the other hand, anon-Newtonian fluid may exhibiting an increase in force at higher strain(i.e, strain hardening) while still exhibit a linear force—strainrelationship at lower strain (i.e, Newtonian-like).

The strain experienced by a fluid element in a non-Newtonian fluid isdependent on its kinematic history, that is$\underset{0}{ɛ = {\int{{ɛ \cdot \left( t^{\prime} \right)}{\partial t^{\prime}}}}}$

This time or history dependent strain is called the Hencky strain(ε_(H)). For an ideal homogeneous uniaxial elongation, the strain rateexperienced by every fluid element is equal to the strain imposed by theapplied stress, such as the stresses applied externally by theinstrument, device or process. In such an ideal case, the Hencky straincorrelates directly with the sample deformation/elongation

ε_(H) =ln(L/L _(o))

Such an ideal strain response to applied stress is most often observedin Newtonian fluids.

The Trouton ratio (Tr) is often used to express the extensional flowbehavior. The Trouton ratio is defined as the ratio between theextensional viscosity (η_(e)) and the shear viscosity (η_(s)),

Tr=η _(e)(ε*,t)/η_(s)

wherein the extensional viscosity η_(e) is dependent on the deformationrate (ε*) and time (t). For a Newtonian fluid, the uniaxial extensionTrouton ratio has a constant value of 3. For a non-Newtonian fluid, theextensional viscosity is dependent on the deformation rate (ε*) and time(t).

Shear viscosity (η_(s)) relates to the melt processability of the starchcomposition using standard polymer processing techniques, such asextrusion, blow molding, compression molding, injection molding and thelike. A starch composition having a shear viscosity, measured accordingto the Test Method disclosed hereinafter, of less than about 30 Pa·s,preferably from about 0.1 to about 10 Pa·s, more preferably from about 1to about 8 Pa·s, is useful in the melt attenuation processes herein.Some starch compositions herein may have low melt viscosity such thatthey may be mixed, conveyed, or otherwise processed in traditionalpolymer processing equipment typically used for viscous fluids, such asa stationary mixer equipped with metering pump and spinneret. The shearviscosity of the starch composition may be effectively modified by themolecular weight and molecular weight distribution of the starch, themolecular weight of the high polymer, and the amount of plasticizersand/or solvents used. It is found that reducing the average molecularweight of the starch is an effective way to lower the shear viscosity ofthe composition.

It is generally known that melt shear viscosity is a material propertyuseful for evaluating melt processability of the material in traditionalthermoplastic processes such as injection molding or extrusion. Forconventional fiber spinning thermoplastics such as polyolefins,polyamides and polyesters, there is a strong correlation between shearviscosity and extensional viscosity of these conventional thermoplasticmaterials and blends thereof. That is, the spinnability of the materialcan be determined simply by the melt shear viscosity, even though thespinnablity is a property controlled primarily by melt extensionalviscosity. The correlation is quite robust such that the fiber industryhas relied on the melt shear viscosity in selecting and formulating meltspinnable materials. The melt extensional viscosity has rarely been usedas an industrial screening tool.

It is therefore surprising to find that the starch compositions of thepresent invention do not exhibit such a correlation between shear andextensional viscosities. Specifically, when a high polymer selectedaccording to the present invention is added to a starch composition, theshear viscosity of the composition remains relatively unchanged, or evendecreases slightly. Based on conventional wisdom, such a starchcomposition would exhibit decreased melt processability and would not besuitable for melt extensional processes. However, it is surprisinglyfound that the starch composition herein shows a significant increase inextensional viscosity when even a small amount of high polymer is added.Consequently, the starch composition herein is found to have enhancedmelt extensibility and is suitable for melt extensional processes (e.g.,blow molding, spun bonding, blown film molding, foam molding, and thelike).

Extensional or elongational viscosity (η_(e)) relates to meltextensibility of the composition, and is particularly important forextensional processes such as fiber, film or foam making. Theextensional viscosity includes three types of deformation: uniaxial orsimple extensional viscosity, biaxial extensional viscosity, and pureshear extensional viscosity. The uniaxial extensional viscosity isimportant for uniaxial extensional processes such as fiber spinning,melt blowing, and spun bonding. The other two extensional viscositiesare important for the biaxial extension or forming processes for makingfilms, foams, sheets or parts. It is found that the properties of thehigh polymers have a significant effect on melt extensional viscosity.The high polymers useful for enhancing the melt extensibility of thestarch composition of the present invention are typically high molecularweight, substantially linear polymers. Moreover, high polymers that aresubstantially compatible with starch are most effective in enhancing themelt extensibility of the starch composition.

It has been found that starch compositions useful for melt extensionalprocesses typically hasve their extensional viscosity increased by afactor of at least 10 when a selected high polymer is added to thecomposition. Typically, the starch compositions of present inventionshow an increase in the extensional viscosity of about 10 to about 500,preferably of about 20 to about 300, more preferably from about 30 toabout 100, when a selected high polymer is added.

It has also been found that melt processable compositions of the presentinvention typically have a Trouton ratio of at least about 3. Typically,the Trouton ratio ranges from about 10 to about 5,000, preferably fromabout 20 to about 1,000, more preferably from about 30 to about 500,when measured at 90° C. and 700 s⁻¹.

When the starch composition of the present composition is subjected toan uniaxial extensional process, a draw ratio, expressed in (D_(o) ²/D²)wherein D_(o) is the diameter of filament before drawing and D is thediameter of the drawn fiber, greater than 1000 can be easily achieved.The starch composition of the present invention typically achieves adraw ratio from about 100 to about 10,000, preferably greater than about1,000, more preferably greater than about 3,000 and most preferablygreater than about 5,000. More specifically, the starch composition ofthe present invention has sufficient melt extensibility to be melt drawnto fine fibers having a finite average diameter of less than 50 microns,preferably less than 25 microns, more preferably less than 15 microns,even more preferably less than 10 microns, and most preferably less than5 microns.

When the starch composition of the present invention is subjected to abiaxial extensional process, the enhanced melt extensibility of thecomposition allows it to be melt drawn to films having a finite averagecaliper of less than 0.8 mils, preferably less than 0.6 mils, morepreferably less than 0.4 mils, even more preferably less than 0.2 mils,and most preferably less than 0.1 mils.

The starch composition herein is processed in a flowable state, whichtypically occurs at a temperature at least equal to or higher than itsmelting temperature. Therefore, the processing temperature range iscontrolled by the melting temperature of the starch composition, whichis measured according to the Test Method described in detail herein. Themelting temperature of the starch composition herein ranges from about80 to 180° C., preferably from about 85 to about 160° C., and morepreferably from about 90 to about 140° C. It is to be understood thatsome starch compositions may not exhibit pure “melting” behavior. Asused herein, the term “melting temperature” means the temperature or therange of temperature at or above which the composition melts or softens.

Exemplary uniaxial extensional processes suitable for the starchcompositions include melt spinning, melt blowing, and spun bonding.These processes are described in detail in U.S. Pat. No. 4,064,605,issued on Dec. 27, 1977 to Akiyama et al.; U.S. Pat. No. 4,418,026,issued on Nov. 29, 1983 to Blackie et al.; U.S. Pat. No. 4,855,179,issued on Aug. 8, 1989 to Bourland et al.; U.S. Pat. No. 4,909,976,issued on Mar. 20, 1990 to Cuculo et al.; U.S. Pat. No. 5,145,631,issued on Sep. 8, 1992 to Jezic; U.S. Pat. No. 5,516,815, issued on May14, 1996 to Buehler et al.; and U.S. Pat. No. 5,342,335, issued on Aug.30, 1994 to Rhim et al.; the disclosure of all of the above areincorporated herein by reference. The resultant products may find use infilters for air, oil and water; vacuum cleaner filters; furnace filters;face masks; coffee filters, tea or coffee bags; thermal insulationmaterials and sound insulation: materials; nonwovens for one-time usesanitary products such as diapers, feminine pads, and incontinencearticles; biodegradable textile fabrics for improved moisture absorptionand softness of wear such as microfiber or breathable fabrics; anelectrostatically charged, structured web for collecting and removingdust; reinforcements and webs for hard grades of paper, such as wrappingpaper, writing paper, newsprint, corrugated paper board, and webs fortissue grades of paper such as toilet paper, paper towel, napkins andfacial tissue; medical uses such as surgical drapes, wound dressing,bandages, dermal patches and self-dissolving sutures; and dental usessuch as dental floss and toothbrush bristles. The fibrous web may alsoinclude odor absorbants, termite repellants, insecticides, rodenticides,and the like, for specific uses. The resultant product absorbs water andoil and may find use in oil or water spill clean-up, or controlled waterretention and release for agricultural or horticultural applications.The resultant starch fibers or fiber webs may also be incorporated intoother materials such as saw dust, wood pulp, plastics, and concrete, toform composite materials, which can be used as building materials suchas walls, support beams, pressed boards, dry walls and backings, andceiling tiles; other medical uses such as casts, splints, and tonguedepressors; and in fireplace logs for decorative and/or burning purpose.

The melt rheological behavior of the present starch composition alsomakes it suitable for use in conventional thermoplastic processes thatinvolves biaxial extension of the material. By having the proper meltshear viscosity and biaxial extensional viscosity, the starchcompositions of the present invention may substantially reduce theoccurrence of tearing, surface defects, and other breakdowns or defectsthat interrupt continuous processes and produce unsatisfactory products.These processes include blow molding, blown film extrusion orcoextrusion, vacuum forming, pressure forming, compression molding,transfer molding and injection molding. Nonlimiting examples of theseprocesses are described in details in U.S. Pat. No. 5,405,564,issued onApr. 11, 1995 to Stepto et al.; U.S. Pat. No. 5,468,444, issued on Nov.21, 1995 to Yazaki et al.; U.S. Pat. No. 5,462,982, issued on Oct. 31,1995 to Bastioli et al.; the disclosure of all of the above are herebyincorporated by reference. The articles produced by these processesinclude sheets, films, coatings, laminates, pipes, rods, bags, andshaped articles (such as bottles, containers). The articles may find useas bags such as shopping bags, grocery bags, and garbage bags; pouchesfor food storage or cooking; microwavable containers for frozen food,and pharmaceutical uses such as capsules or coatings for medicine. Thefilms may be substantially transparent for use as food wraps, shrinkwraps or windowed envelopes. The films may also be further processed foruse as an inexpensive, biodegradable carrier for other materials such asseeds or fertilizers. Adhesives may be applied to the films or sheetsfor other uses such as labels.

The starch compositions of the present invention may also be made into afoamed structure by controlled removal of the volatile components (e.g.,water, polar solvents). However, foaming or expanding agents aregenerally incorporated to produce articles having foamed or porousinternal structure. Exemplary foaming or expanding agents include carbondioxide, n-pentane, and carbonate salts such as sodium bicarbonate,either alone or in combination with a polymeric acid which has lateralcarboxyl groups (e.g., polyacrylic acid, ethylene-acrylic copolymer).Nonlimiting examples of the foaming and forming processes are describedin U.S. Pat. No. 5,288,765, issued on Feb. 22, 1994 to Bastioli et al.;U.S. Pat. No. 5,496,895, issued on Mar. 5, 1996 to Chinnaswamy et al.;U.S. Pat. No. 5,705,536, issued on Jan. 6, 1998 to Tomka; and U.S. Pat.No. 5,736,586, issued on Apr. 7, 1998 to Bastioli et al.; thedisclosures of which are hereby incorporated by reference. The resultantproducts may find use in egg cartons; foamed cups for hot beverages;containers for fast food; meat trays; plates and bowls for one-time usesuch as at picnic or parties; packaging materials, either loose-fill ormolded to conform to the packed article (e.g., a computer shippingpackage); thermal insulation materials; and noise insulation or soundproofing materials.

Test Methods

A. Shear Viscosity

The shear viscosity of the composition is measured using a rotationalviscometer (Model DSR 500, manufactured by Rheometrics). A preheatedsample composition is loaded into the barrel section of the rheometer,and substantially fills the barrel section (about 60 grams of sample isused). The barrel is held at a test temperature of 90° C. After theloading, air generally bubbles to the surface and does create problemsfor the run. For a more viscous samples, compaction prior to running thetest may be used to rid the molten sample of entrapped air. Theviscometer is programmed to ramp the applied stress from 10 dyne/cm to5000 dyne/cm. The strain experienced by the sample is measure by astrain gauge. The apparent viscosity of the composition can be derivedtherefrom. Then log (apparent shear viscosity) is plotted against log(shear rate) and the plot is fitted by the power law η=K γ^(n−1),wherein K is a material constant, γ is the shear rate. The reportedshear viscosity of the starch composition herein is an extrapolation toa shear rate of 700 s⁻¹ using the power law relation.

B. Extensional Viscosity

The extensional viscosity is measured using a capillary rheometer (ModelRheograph 2003, manufactured by Geottfert). The measurements areconducted using an orifice die having a diameter D of 0.5 mm and alength L of 0.25 mm (i.e., L/D=0.5). The die is attached to the lowerend of a barrel, which is held at a test temperature of 90° C. Apreheated sample composition is loaded into the barrel section of therheometer, and substantially fills the barrel section. After theloading, air generally bubbles to the surface and does create problemsfor the run. For more viscous compositions, compaction prior to runningthe test may be used to rid the molten sample of entrapped air. A pistonis programmed to push the sample from the barrel through the orifice dieat a chosen rate. As the sample goes from the barrel through the orificedie, the sample experiences a pressure drop. An apparent viscosity canbe obtained from the pressure drop and the flow rate of the samplethrough the orifice die. Corrections are often applied to the apparentviscosity following procedures generally known in the art. A shearcorrection factor and Cogswell equation are applied to the calculationof the extensional viscosity. The corrected extensional viscosity at 700s⁻¹ is reported.

It is known that the extensional viscosity can be measured using anorifice die and applying the correction factors, following the methoddescribed herein. More details of extensional viscosity measurements aredisclosed in S. H. Spielberg et al., The Role Of End-Effects OnMeasurements Of Extensional Viscoisty In Filament Stretching Rheometers,Journal of Non-Newtonian Fluid Mechanics, Vol. 64, 1996, p. 229-267;Bhattacharya, et al., Uniaxial Extensional Viscoisty During ExtrusionCooking From Entrance Pressure Drop Method, Journal of Food Science,Vol. 59, No. 1, 1994, p. 221-226; both are hereby incorporated byreference. It is also known that the extensional viscosity can bemeasured using a hyperbolic or semi-hyperbolic die. Detailed disclosureof extensional viscosity measurements using a semi-hyperbolic die isdisclosed in U.S. Pat. No. 5,357,784, issued Oct. 25, 1994 to Collier,the disclosure of which is incorporated herein by reference.

C. Molecular Weight and Molecular Weight Distribution

The weight-average molecular weight (Mw) and molecular weightdistribution (MWD) of starch are determined by Gel PermeationChromatography (GPC) using a mixed bed column. Parts of the instrumentare as follows:

Pump Waters Model 600E System controller Waters Model 600E AutosamplerWaters Model 717 Plus Column PL gel 20 μm Mixed A column (gel molecularweight ranges from 1,000 to 40,000,000) having a length of 600 mm and aninternal diameter of 7.5 mm. Detector Waters Model 410 DifferentialRefractometer GPC software Waters Millenium ® software

The column is calibrated with Dextran standards having molecular weightsof 245,000; 350,000; 480,000; 805,000; and 2,285,000. These Dextrancalibration standards are available from American Polymer StandardsCorp., Mentor, Ohio. The calibration standards are prepared bydissolving the standards in the mobile phase to make a solution of about2 mg/ml. The solution sits undisturbed overnight. Then it is gentlyswirled and filtered through a syringe filter (5 μm Nylon membrane,Spartan-25, available from VWR) using a syringe (5 ml, Norm-Ject,available from VWR).

The starch sample is prepared by first making a mixture of 40 wt %starch in tap water, with heat applied until the mixture gelatinizes.Then 1.55 grams of the gelatinized mixture is added to 22 grams ofmobile phase to make a 3 mg/ml solution which is prepared by stirringfor 5 minutes, placing the mixture in an oven at 105° C. for one hour,removing the mixture from the oven, and cooling to room temperature. Thesolution is filtered using the syringe and syringe filter as describedabove.

The filtered standard or sample solution is taken up by the autosamplerto flush out previous test materials in a 100 μl injection loop andinject the present test material into the column. The column is held at70° C. The sample eluded from the column is measured against the mobilephase background by a differential refractive index detector held at 50°C. and with the sensitivity range set at 64. The mobile phase is DMSOwith 0.1% w/v LiBr dissolved therein. The flow rate is set at 1.0 ml/minand in the isocratic mode (i.e., the mobile phase is constant during therun). Each standard or sample is run through the GPC three times and theresults are averaged.

The average molecular weight of the high polymer is provided by thematerial suppliers.

D. Thermal Properties

Thermal properties of the present starch compositions are determinedusing a TA Instruments DSC-2910 which has been calibrated with an indiummetal standard, which has an melting temperature (onset) of 156.6° C.and a heat of melting of 6.80 calories per gram, as reported in thechemical literature. Standard DSC operating procedure per manufacturer'sOperating Manual is used. Due to the volatile evolution (e.g., watervapor) from the starch composition during DSC measurement, a high volumepan equipped with an o-ring seal is used to prevent the escape ofvolatiles from the sample pan. The sample and an inert reference(typically an empty pan) are heated at the same rate in a controlledenvironment. When an actual or pseudo phase change occurs in the sample,the DSC instrument measures the heat flow to or from the sample versusthat of the inert reference. The instrument is interfaced with acomputer for controlling the test parameters (e.g., the heating/coolingrate), and for collecting, calculating and reporting the data.

The sample is weighed into a pan and enclosed with an o-ring and a cap.A typical sample size is 25-65 milligrams. The enclosed pan is placed inthe instrument and the computer is programmed for the thermalmeasurement as follows:

1. equilibrate at 0° C.;

2. hold for 2 minutes at 0° C.;

3. heat at 10° C./min to 120° C.;

4. hold for 2 minutes at 120° C.;

5. cool at 10° C./min to 30° C.;

6. equilibrate at ambient temperature for 24 hours, the sample pan maybe removed from the DSC instrument and placed in a controlledenvironment at 30° C. in this duration;

7. return sample pan to the DSC instrument and equilibrate at 0° C.;

8. hold for 2 minutes;

9. heat at 10° C./min to 120° C.;

10. hold for 2 minutes at 120° C.;

11. cool at 10° C./min to 30° C. and equilibrate; and

12. remove the used sample.

The computer calculates and reports the thermal analysis result asdifferential heat flow (ΔH) versus temperature or time. Typically thedifferential heat flow is normalized and reported on per weight basis(i.e, cal/mg). Where the sample exhibits a pseudo phase transition, suchas a glass transition, a differential of the ΔH v. time/temperature plotmay be employed to more easily determine a glass transition temperature.

E. Water Solubility

A sample composition is made by mixing the components with heat andstirring until a substantially homogeneous mixture is formed. The meltcomposition is cast into a thin film by spreading it over a Teflon®sheet and cooling at ambient temperature. The film is then driedcompletely (i.e., no water in the film/composition) in an oven at 100°C. The dried film is then equilibrated to room temperature. Theequilibrated film is ground into small pellets.

To determine the % solids in the sample, 2 to 4 grams of the groundsample is placed in a pre-weighed metal pan and the total weight of panand sample is recorded. The weighed pan and sample is palced in a 100°C. oven for 2 hours., and then taken out and weighed immediately. The %solids is calculated as follows:${\% \quad {Solids}} = {\frac{\left( {{{{dried}\quad {weight}\quad {of}\quad {ground}\quad {sample}}\&}\quad {pan}\text{-}{weight}\quad {of}\quad {pan}} \right)}{\left( {{{{first}\quad {weight}\quad {of}\quad {ground}\quad {sample}}\&}\quad {pan}\text{-}{weight}\quad {of}\quad {pan}} \right)} \times 100}$

To determine the solubility of the sample composition, weigh 10 grams ofground sample in a 250 mL beaker. Add deionized water to make a totalweight of 100 grams. Mix the sample and water on a stir plate for 5minutes. After stirring, pour at least 2 mL of stirred sample into acentrifuge tube. Centrifuge 1 hour at 20,000 g at 10° C. Take thesupernatant of the centrifuged sample and read the refractive index. The% solubility of the sample is calculated as follows:.${\% \quad {Soluble}\quad {Solids}} = \frac{\left( {{Refractive}\quad {Index}\quad \#} \right) \times 1000}{\% \quad {Solids}}$

F. Caliper

Prior to testing, the film sample is conditioned at a relative humidityof 48%-50% and at a temperature of 22° C. to 24° C. until a moisturecontent of about 5% to about 16% is achieved. The moisture content isdetermined by TGA (Thermo Gravimetric Analysis). For Thermal GravimetricAnalysis, a high resolution TGA2950 Termogravimetric analyzer from TAInstruments is used. Approximately 20 mg of sample is weighed into a TGApan. Following the manufacturer's instructions, the sample and pan areinserted into the unit and the temperature is increased at a rate of 10°C./minute to 250° C. The % moisture in the sample is determined usingthe weight lost and the initial weight as follows:${\% \quad {Moisture}} = {\frac{{{Start}\quad {Weight}} - {{{Weight}@250^{{^\circ}}}\quad {C.}}}{{Start}\quad {Weight}}*100\quad \%}$

Preconditioned samples are cut to a size greater than the size of thefoot used to measure the caliper. The foot to be used is a circle withan area of 3.14 square inches.

The sample is placed on a horizontal flat surface and confined betweenthe flat surface and a load foot having a horizontal loading surface,where the load foot loading surface has a circular surface area of about3.14 square inches and applies a confining pressure of about 15 g/squarecm (0.21 psi) to the sample. The caliper is the resulting gap betweenthe flat surface and the load foot loading surface. Such measurementscan be obtained on a VIR Electronic Thickness Tester Model II availablefrom Thwing-Albert, Philadelphia, Pa. The caliper measurement isrepeated and recorded at least five times. The result is reported inmils.

The sum of the readings recorded from the caliper tests is divided bythe number of readings recorded. The result is reported in mils.

EXAMPLES

The materials used in the Examples are as follows:

Crystal Gum® is a modified starch having a weight-average molecularweight of 100,000; Nadex® is a modified starch having a weight averagemolecular weight of 2,000; and Instant-n Oil® is a modified starchhaving a weight average molecular weight of 800,000; all are availablefrom National Starch and Chemicals Corp., Bridgewater, N.J.

Superfloc® A-130 is a carboxylated polyacrylamide having aweight-average molecular weight of 12,000,000 to 14,000,000 and isavailable from Cytec Co., Stamford, Conn.

Nonionic polyacrylamides PAM-a and PAM-b having a weight-averagemolecular weight of 15,000,000, and 5,000,000 to 6,000,000,respectively, are available from Scientific Polymer Products, Inc.,Ontario, N.Y.

Polyethyleneimine having a weight-average molecular weight of 750,000 isavailable from Aldrich Chemical Co., Milwaukee, Wis.

Parez® 631 NC is a low molecular weight glyoxylated polyacrylamide, andParez® 802 is a low molecular weight glyoxylated urea resin, both areavailable from Cytec Co., Stamford, Conn.

Pluronic® F87 is nonionic poloxomer, available form BASF corp.,Parsippany, N.J.

Urea, sucrose and glyoxal (in 40% solution in water) are available fromAldrich Chemical Co., Milwaukee, Wis.

Example 1

A melt processable composition of the invention is prepared by mixing 45wt % starch (Crystal Gum), 40.5 wt % urea, 4.5 wt % sucrose, and 9.8 wt% free water, and manually stirring to form a slurry. Polyacrylamide(PAM-a, Mw=15,000,000) is dissolved in water to form a PAM aqueoussolution. An aliquot of the polymer/water solution is added to theslurry. Water in the slurry is then evaporated until the weight percentof polyacrylamide in the final mixture is 0.2 wt %.

The composition has a shear viscosity of 0.65 Pa·s and an extensionalviscosity of 1863.2 Pa·s, at 700s⁻¹ and 90° C.

Comparative Example 1b

A comparative starch composition is prepared according to Example 1except no polyacrylamide is added to the composition. The compositionhas a shear viscosity of 1.35 Pa·s and an extensional viscosity of 43.02Pa·s, at 700s⁻¹ and 90° C. Example 1 and Comparative Example 1bdemonstrate that addition of a small amount of high polymer decreasesthe shear viscosity slightly and significantly increases the extensionalviscosity.

Example 2

A melt processable composition of the invention is prepared by mixing 50wt % starch (Crystal Gum), 30 wt % urea, 1.5 wt % sucrose, and 18.5 wt %free water, and manually stirring to form a slurry. Polyacrylamide(Superfloc A-130, Mw=12-14,000,000) is dissolved in water to form a PAMaqueous solution. An aliquot of the polymer/water solution is added tothe slurry. Water in the slurry is then evaporated until the weightpercent of polyacrylamide in the final mixture is 0.003 wt %.

The composition has a shear viscosity of 1.12 Pa·s and an extensionalviscosity of 46.0 Pa·s, at 700s⁻¹ and 90° C.

Comparative Example 2b

A comparative starch composition is prepared according to Example 2except no polyacrylamide is added to the composition. The compositionhas a shear viscosity of 1.23 Pa·s and an extensional viscosity of 0.69Pa·s, at 700s⁻¹ and 90° C. Example 2 and Comparative Example 2bdemonstrate that addition of a small amount of high polymer decreasesthe shear viscosity slightly and significantly increases the extensionalviscosity.

Example 3

A torque rheometer having a melt blowing die is used to process thecomposition of Example 1. The torque rheometer is illustrated in FIG. 1.The torque rheometer assembly 100 includes a drive unit 110 (ModelRheocord 90 available from Haake GmbH), a barrel 120 partitioned intofour temperature zones 122, 124, 126 and 128, a feed port 121, and amelt spinning die assembly 130. Twin screw elements 160 (model TW100,from Haake GmbH) are attached to the drive until 110 and disposed withinthe barrel 120. A six-inch wide melt blowing die assembly 130 (availablefrom JM Laboratories, Dawsonville, Ga.) is connected to the end of thebarrel via a pump 140. The die assembly has a spinneret plate which has52 holes per linear inch and a hole diameter of 0.015″ (0.0381 cm),surrounded by a 0.02″ wide air passageway 152, from which a highvelocity air stream 150 impinges the extruded filaments just below thespinneret plate. The air stream has the effect of simultaneously blowingthe filaments away from the spinneret and attenuating the filaments.

The composition of is prepared (as described in Example 1) by mixing 45wt % starch (Crystal Gum), 0.2 wt % polyacrylamide (PAM-a), 40.5 wt %urea, 4.5 wt % sucrose, and 9.8 wt % water. The mixture is gravity-fedvia feed port 121 into a torque rheometer. The torque rheometer and dieassembly are set as follows:

Barrel Temperature Zone 122 70° C. Zone 124 90° C. Zone 126 90° C. Zone128 90° C. Torque 100 rpm Die Temperature 126.7° C. Air Temperature126.7° C. Air Pressure 35 psi Pump  40 rpm

The mixture is conveyed from the extruder through the pump into the meltblowing die. The resulting attenuated filaments (or fine fibers) of theinvention have fiber diameters ranging from 8 to 40 microns.

Note that the weight percent starch in the melt processable compositionincludes the weight of starch and the weight of bound water (which is onthe average about 8 wt % of the starch). It is to be understood that theas-prepared compositions are used for uniaxial and biaxial extensionalprocesses. However, most of the water is lost during the melt process,and the resulting starch fiber, film or like product contains little orno free water. The resulting product does contain some bound water(possible by absorbing moisture from ambient environment). Therefore,the composition of the resulting product may be more appropriatelyexpressed by its solid components, calculated on a dry solid basis. Forexample, to calculate, on a dry solid basis, the composition of thefiber made according to Example 3, one would take out the 9.8 wt % freewater from the overall composition and the 8 wt % bound water from thestarch, then 35 normalize the remaining solid content to 100%. Thus, thecomposition of the fiber of Example 3 calculated on a dry solid basiswould be 47.8 wt % starch solid (without bound water), 0.23 wt %polyacrylamide, 46.8 wt % urea and 5.2 wt % sucrose.

Example 4

The composition of Example 2 is melt blown into fine fibers of theinvention. FIG. 3a is the Scanning Electron Micrographs of fine starchfibers made from the composition of Example 2 using the processdescribed in Example 3, shown on a 200 micron scale. FIG. 3b is theScanning Electron Micrographs of the same starch fibers shown on a 20micron scale. Both figures show that starch fibers of Example 4 have afairly consistent fiber diameter of about 5 microns.

Example 5

Fifteen grams of starch (Crystal Gum, Mw=100,000) and fifteen grams offree water are mixed together at 80° C. with manual stirring until themixture becomes substantially homogeneous or gelatinizes. A high polymer(PAM-a, Mw=15,000,000) is dissolved in free water to form a PAM aqueoussolution of known concentration. An aliquot of the polymer/watersolution is added to the starch/water mixture such that the overallmixture contains 0.006 grams of PAM-a. Then the overall mixture isheated to evaporate water until the weight of the final mixture (starch,PAM-a and water) equals 30 grams. This mixture is subjectively shown tohave suitable melt extensibility for drawing fibers.

Examples 6-8

Mixtures of starch (Crystal Gum), high polymer and water are prepared inthe same manner as in Example 5. The final compositions of these mixtureare shown below.

Mw Ex-6 Ex-7 Ex-8 Starch Crystal 100,000 wt % 49.99 49.99 46.92 GumPoly- Superfloc 12-14,000,000 wt % 0.02 acrylamide A-130 PAM-b5-6,000,000 wt % 0.02 Polyethylene- 750,000 wt % 6.17 imine Water wt %49.99 49.99 46.91

These compositions of the invention are subjectively shown to havesuitable melt extensibility for drawing fibers.

Examples 9-11

The following compositions are prepared in the same manner as Example 1.

Mw Ex-9 Ex-10 Ex-11 Starch Crystal 100,000 wt % 41.54 20.77 20.77 GumNadex 2,000 wt % 20.77 Instant-n 800,000 wt % 20.77 Oil Poly- PAM-a15,000,000 wt % 0.08 0.08 0.08 acrylamide Urea wt % 6.23 6.23 6.23Sucrose wt % 6.23 6.23 6.23 Parez wt % 1.04 1.04 1.04 631 NC Water wt %44.88 44.88 44.88

These compositions of the invention are expected to have suitable meltextensibility for drawing fibers. And where the water has been adjustedto about pH 2, the resulting fibers are expected to have a watersolubility of less than 30%, based on the test method disclosed herein.

Example 12

A melt processable composition is prepared by mixing 45 wt % starch(Crystal Gum), 0.2 wt % polyacrylamide (PAM-a), 40.5 wt % urea, 4.5 wt %sucrose, and 9.8 wt % water to form a slurry. The composition is meltblown into fine fibers using a torque rheometer as shown in FIG. 1 inthe manner described in Example 3, except the mixture is meter-fed intothe torque rheometer. The torque rheometer and die assembly are set asfollows:

Barrel Temperature Zone 122 70° C. Zone 124 90° C. Zone 126 90° C. Zone128 90° C. Torque 140 rpm Feed Rate 16 gm/min Die Temperature 137.80° C.Air Temperature 137.80° C. Air Pressure 50 psi Pump  40 rpm

The resulting attenuated filaments (or fine fibers) of the inventionhave fiber diameters ranging from 10 to 30 microns. The fibers are airlaid onto a papermaking forming fabric as described in U.S. Pat. No.4,637,859, with the fabrics of U.S. Pat. Nos. 5,857,498, 5,672,248,5,211,815 and 5,098,519, all incorporated herein by reference, alsobeing judged suitable for this purpose.

Example 13

The resultant web from the air-laying process of Example 12 is testedfor oil absorbency. A drop of a commercially available motor oil (SAE 20grade, by the Society of Automobile Engineers' designation) is placed onthe web and on a commercially available paper towel, respectively, forcomparison of oil absorbency. The web shows an improved oil absorbencyover that of the commercial paper towel in the following aspects: (1)the web absorbs oil faster than the commercial paper towel, as shown bya shorter residence time on the surface of the web; and (2) after 30seconds, the web has a spot size of about 1.5 to 2 times larger indiameter than that of the commercial paper towel.

Example 14

This example illustrates that the starch composition of the presentinvention can be made into building materials, e.g., pressed board. Amelt processable composition is prepared by mixing 60 wt % starch(Crystal Gum), 0.1 wt % polyacrylamide (SP2), 2 wt % urea, 2 wt %sucrose, 1.5 wt % Parez 631 NC and 34.4 wt % water (adjusted to pH 2with sulfuric acid) to form a slurry. The slurry is fed in to a torquerheometer (Model Rheocord 90) as illustrated in FIG. 1 and operatedunder the conditions as described in Example 12 above, except a singlecapillary die (having a 1 mm diameter and a temperature of 90° C.) isused instead of a melt spinning die. The extruded strand is dusted withsaw dust or wood shavings while still wet and sticky. The dusted strandsare compressed together to form a log. The log is dried at 40° C. in aforced air oven for two hours to get rid of the residual water from thestarch composition. The final product is a log of 47.8 wt % saw dust and52.2 wt % dried starch composition.

Example 15

This example illustrates that the present invention can be incorporatedinto structural materials as reinforcements. Though this example usesfibers made from a composition without high polymers. It is believedthat when a composition of the present invention is used, the productwould show better or equivalent performances.

A comparative cement sample is prepared as follows: 5 parts ofcommercially available Quikrete Anchoring cement are mixed with 1.5 partclean tap water until a thick syrup consistency is obtained. Within 5minutes of mixing, the cement was introduced into cylindrical molds inorder to obtain a constant dimension sample for evaluation. Thin wallmolds 5″ long and 0.23″ in inner diameter (i.e., commercially availablestraws) are filled by driving the pasty cement mixture up from thebottom. This filling method eliminates air inclusion in the finishedsample. The samples are allowed to cure for 5 days prior to evaluation.The mold is carefully scored on the outer surface so as not to damagethe sample inside, then the mold is peeled away to retrieve thecomparative sample (Example 15b).

A melt processable composition is prepared by mixing 45 wt % starch(Durabond®, available from National Starch and Chemicals Corp.,Bridgewater, N.J.), 15 wt % urea, 15 wt % sorbitol, and 25 wt % water toform a slurry. The slurry is fed in to a torque rheometer (ModelRheocord 90) as illustrated in FIG. 1 and operated under the conditionas described in Example 14 above. The fibers are about 0.02″ in diameterand are cut to 1″ in length for use herein. The extruded, thinspaghetti-like strands are incorporated into cement as follows: 5 partsof commercially available Quikrete Anchoring cement are mixed with 1.5part clean tap water and 0.5% (on a dry weight basis) starch fibers. Theadditional amount of water added herein is required to achieve thecomparable consistency as the comparative sample above. The sample moldsare filled and the samples (Example 15) are cured and retrieved in thesame manner as above.

The samples are subjectively evaluated by bending to failure by hand.Example 15 are subjectively judged to be slightly weaker than thecomparative Example 15b. Example 15 has an apparent density of 1.46g/linear inch while comparative Example 15b has an apparent density of1.48 g/linear inch. Therefore, it is demonstrated that Example 15 offersthe benefits of light weight and lower cost (on a volume basis).

Example 16

This example illustrates that the composition of the present inventioncan prophetically be made into a controlled water release material whenmixed with potting soil. The controlled water release is useful forhorticultural and agricultural plants which thrive in a relatively lowhumidity environment and/or infrequent watering. A melt processablecomposition is prepared by mixing 50 wt % starch (Durabond®, availablefrom National Starch and Chemicals Corp., Bridgewater, N.J.), 0.1 wt %polyacrylamide (SP2®), 15 wt % urea, 15 wt % sorbitol, 1.5 wt % Parez®and 18.4 wt % water to form a slurry. The slurry is fed in to a torquerheometer (Model Rheocord 90) as illustrated in FIG. 1 and operatedunder the condition as described in Example 14 above. The extruded, thinspaghetti-like strands are allowed to dry before mixing with pottingsoil. The ratio of starch-based strand to potting soil depends on therequirements of various types of plants. Generally, 10 wt % ofstarch-based strands in potting soil shows satisfactory waterholding/release results.

Examples 17-19 use films made from compositions without the benefit ofhigh polymers. It is believed that when a composition of the presentinvention is used in each of these examples, the resultant product wouldshow beneficial improvements in properties, e.g., lower caliper, greaterflexibility.

Example 17

This example illustrates that the compositions of the invention can bemade into thin films, using a Werner & Pfleiderer ZSK-30 co-rotatingtwin-screw extruder with a L/D ratio of 40. The screw configurationconsists of four kneading sections and five conveying sections. Theextruder barrel consisted of an unheated feed zone followed by sevenheated zones, which are designated consecutively as Zones A, B, 1, 2, 3,4 and 5. The barrel is controlled to the temperature profile summarizedbelow, and the screw speed is set to 150 rpm.

Zone A B 1 2 3 4 5 Temperature ° C. 50 50 50 95 95 95 95

A melt processable composition is prepared by metering the solidmaterials into the extruder with a K2V-T20 volumetric feeder (availablefrom K-Tron Inc., Pitman, N.J.) and metering the liquid material intoZone 1 of the extruder with a mini pump (available from Milton-Roy,Ivyland, Pa.). The components are: 44 wt % starch (Durabond® A,available from National Starch and Chemicals Corp., Bridgewater, N.J.),18 wt % urea, 18 wt % sucrose, and 20 wt % water. The mixture isconveyed from the extruder into a Zenith B-9000 gear pump into asix-inch wide flat film die (available from Killion Extruders, CedarGrove, N.J.) at a flow rate of 33 cm³/min, wherein the gear pump ismaintained at 96° C., the film die is maintained at 94° C. and the dieopening is set at 15 mils. The resultant film is extruded onto a 12-inchwide chill roll (available from Killion Extruders) which is maintainedat 37° C. The film is then wound onto a paper core at a speed of 5 fpm.The resultant film is about 1 mil in thickness, slightly tacky to thetouch, and exhibits excellent flexibility (i.e., it can be repeatedlybent at a 180 degree angle without breaking or forming a dead fold).

Example 18

This example illustrates that the film from Example 17 can be made intoa seed carrier for agricultural applications. The seed carrier film madeaccording to this example provides an inexpensive material that can belaid down to cover and seed a large area effectively. The material holdswater to facilitate the germination of the seeds, and the material isbiodegradable such that no recovery and disposal are required. The filmof Example 17 is placed on a single-sided release paper and sprinkledwith grass seeds available from Midwestern Supply or other garden supplystores. Another sheet of single-sided release paper is placed on top ofthe seeds. The assembly is placed between ¼ inch (0.635 cm) aluminumplates and inserted into a 6 inch by 6 inch (15.24 cm by 15.24 cm)Carver hot press that is preheated to 207° C. The assembly isequilibrated under low/contact pressure for one minute, then pressure isincreased to a maximum pressure of 6000 pounds. The assembly is heldunder the maximum pressure for one minute and quickly depressurized. Theassembly is taken out of the press and cooled to room temperature. Theresulting film composite shows good cohesion between film and seeds suchthat the film composite can be handled without loss of seeds.

Example 19

This example illustrates that the films of Example 17 are fusable suchthat the films can be made into substantially transparent bags/pouchesuseful as sealable food storage pouches, shopping bags, garbage bags,grocery bags, and the like. Two pieces of 4 inch by 4 inch (10.16 cm by10.16 cm) films are overlaid with a piece of release paper interposedbetween them. The release paper should be smaller than the films so thatat least three edges of the films are in direct contact with each other.A Vertrod impulse sealer (Model 24LAB-SP) is used to seal three sides ofthe overlaid films. The sealer is set at 50% voltage, 60 psi pressure, asix second dwell time (one second on and 5 seconds off), and for a totalsealing time of one minute. The resultant bag shows uniform, weldedseals on three sides. The fourth side can optional be sealed to form acompletely sealed pouch.

Example 20

This example illustrates the water-insoluble starch compositions of thepresent invention. A composition is prepared by mixing 50 wt % starch(Crystal Gum), a crosslinking additive (the type and the amount of thecrosslinking additive are shown in the Table below) and a balance ofwater which has been adjusted to pH 2 using sulfuric acid. Where glyoxal(in 40% solution in water) is used, there is no need to adjust the waterpH. The composition and test sample are prepared according to TestMethod for Water Solubility described hereinabove. The results are shownin the Table below:

Solubility: % Additive Parez 631 Glyoxal Parez 802 0.00% 37% 37% 37%0.12% 16% 0.20% 10% 0.25% 28% 48% 0.32% 11% 0.40%  7% 0.50% 16% 16%0.75% 14%  9% 1.00% 14%  6% 1.50% 11%  4%

The disclosures of all patents, patent applications (and any patentswhich issue thereon, as well as any corresponding published foreignpatent applications), and publications mentioned throughout thisdescription are hereby incorporated by reference herein. It is expresslynot admitted, however, that any of the documents incorporated byreference herein teach or disclose the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A substantially homogeneous compositioncomprising: (a) from about 20 to about 99.99 wt % of a starch, whereinthe starch has a weight-average molecular weight ranging from about1,000 to about 2,000,000; and (b) from about 0.001 to about 10 wt % of ahigh polymer, wherein the high polymer is substantially compatible withthe starch, and the weight-average molecular weight of the high polymeris at least 500,000.
 2. The composition of claim 1 wherein from about 20to about 99 wt % of the starch is amylopectin.
 3. The composition ofclaim 1 wherein the weight-average molecular weight of the starch rangesfrom about 1,500 to about 800,000.
 4. The composition of claim 1 whereinthe weight-average molecular weight of the high polymer ranges fromabout 800,000 to about 22,000,000.
 5. The composition of claim 4 whereina solubility parameter of the high polymer and a solubility parameter ofstarch differ by less than 10 MPa^(1/2).
 6. The composition of claim 5wherein the high polymer is selected from the group consisting ofpolyacrylamide and its derivatives; polyacrylic acid, polymethacrylicacid, and their esters; polyvinyl alcohol; polyethyleneimine; copolymersmade from mixtures of monomers of the aforementioned polymers; andmixtures thereof.
 7. The composition of claim 1 further comprising atleast one additive selected from the group consisting of a hydroxylplasticizer having at least one hydroxyl group, a hydroxyl-freeplasticizer, a diluent, and mixtures thereof.
 8. The composition ofclaim 7 wherein the additive further comprises a material selected fromthe group consisting of oxidation agents, cross-linking agents,emulsifiers, surfactants, debonding agents, lubricants, processing aids,optical brighteners, antioxidants, flame retardants, dyes, pigments,fillers, proteins and their alkali salts, biodegradable syntheticpolymers, waxes, low melting synthetic thermoplastic polymers,tacktifying resins, extenders, wet strength resins, and mixturesthereof.
 9. The composition of claim 7 wherein the weight-averagemolecular weight of the starch ranges from about 1,500 to about 800,000,the weight average molecular weight of the high polymer ranges fromabout 800,000 to about 22,000,000, and the solubility parameter of thehigh polymer and the solubility parameter of the starch differ by 10MPa^(1/2).
 10. The composition of claim 9 wherein the high polymer isselected from the group consisting of polyacrylamide and itsderivatives; polyacrylic acid, polymethacrylic acid, and their esters;polyvinyl alcohol; polyethyleneimine; copolymers made from mixtures ofmonomers of the aforementioned polymers; and mixtures thereof.
 11. Asubstantially homogeneous composition prepared by mixing the followingmaterials: (a) from about 20 to about 99.99 wt % of starch, wherein thestarch has a weight-average molecular weight from about 1,000 to about2,000,000; and (b) from about 0.001 to about 10 wt % of a high polymer,wherein the high polymer is substantially compatible with the starch andhas a weight-average molecular weight of at least 500,000.
 12. A processfor preparing a substantially homogeneous composition, the processcomprising the step of: (a) providing a starch having a weight-averagemolecular weight from about 1,000 to about 2,000,000; (b) providing ahigh polymer that is substantially compatible with starch and has aweight-average molecular weight of at least 500,000; (c) providing atleast one additive selected from the group consisting of a hydroxylplasticizer having at least one hydroxyl group, a hydroxyl-freeplasticizer, a diluent, and mixtures thereof; and (d) mixing the starch,the high polymer and the additive together to form a substantiallyhomogeneous composition, wherein the substantially homogeneouscomposition comprises: from about 20 to about 99.99 wt % of the starch,from about 0.001 to about 10 wt % of the high polymer, and a balance ofthe additive.
 13. The process according to claim 12, wherein the step(d) comprises the steps of feeding the starch, the high polymer, and theadditive into an extruder, and extruding a substantially homogeneouscomposition thereof.
 14. A substantially homogeneous compositioncomprising starch, a high polymer, and at least one additive; whereinthe composition has: (a) a melt shear viscosity of less than about 50Pa·s; and (b) an extensional viscosity, which is at least 10 timesgreater than that of a comparative composition having no high polymertherein.
 15. The composition of claim 14 wherein the composition has anuniaxial draw ratio ranging from about 5 to about
 6000. 16. Thecomposition of claim 14 wherein the composition has a meltingtemperature ranging from about 80° C. to about 180° C.
 17. Thecomposition of claim 14 wherein the at least one additive is selectedfrom the group consisting of a hydroxyl plasticizer having at least onehydroxyl group, a hydroxyl-free plasticizer, a diluent and mixturesthereof.
 18. A fiber comprising a substantially homogeneous compositioncomprising: (a) from about 20 to about 99.99 wt % of starch, wherein thestarch has a weight-average molecular weight ranging from about 1,000 toabout 2,000,000; (b) from about 0.001 to about 10 wt % of a highpolymer, wherein the high polymer is substantially compatible withstarch and has a weight-average molecular weight of at least 500,000.19. The fiber of claim 18 wherein the average diameter of the fiber isless than 50 microns.
 20. A film comprising a substantially homogeneouscomposition comprising: (a) from about 20 to about 99.99 wt % of starch,wherein the starch has a weight-average molecular weight ranging fromabout 1,000 to about 2,000,000; (b) from about 0.001 to about 10 wt % ofa high polymer, wherein the high polymer is substantially compatiblewith starch and has a weight-average molecular weight of at least500,000.
 21. The film of claim 20 wherein the film has a thickness ofless than 0.8 mils.